This application is related to the following co-pending applications filed concurrently herewith by the same Applicants and assigned to the same Assignee: “SPACE EFFICIENT MULTI-SHEET BUFFER MODULE AND MODULAR PRINTING SYSTEM” Ser. No. 12/413,876 and “COMBINED SHEET BUFFER AND INVERTER” Ser. No. 12/413,923. The complete disclosures of these co-pending applications are incorporated in their entirety herein by reference.
Embodiments herein generally relate to modular printing systems and, more particularly, to a modular printing system incorporating a double efficiency sheet buffer module.
Modularity in printing systems, such as electrostatographic or other types of printing systems, is known. For example, U.S. patent application Ser. No. 12/211,853 of Bober et al., filed on Sep. 17, 2008, and U.S. patent application Ser. No. 12/331,768 of Mandel et al., filed on Dec. 10, 2008 (both of which are assigned to Xerox Corporation of Norwalk, Conn., USA, and incorporated herein by reference in their entirety) disclose modular printing systems comprising multiple modules (i.e., discrete interchangeable units). Each module comprises one or more functional components (e.g., sheet feeders, printing engines, sheet inverters, sheet buffers, finishers, etc.), each of which is structurally self contained within its own supporting frame and housing (i.e., cabinet).
Often times multi-page documents contain both single color (i.e., monochrome) pages (e.g., text-only pages) and multi-color pages (e.g., pages with colored graphics and/or images only or pages with combinations of text and colored graphics and/or images). Since it is more cost and time efficient to print single color pages using a single color printing engine vice a multi-color printing engine, modular printing systems incorporating heterogeneous printing engine modules (e.g., a single color and multi-color printing engine) in a tightly integrated parallel printing (TIPP) architecture have been developed (e.g., see U.S. patent application Ser. No. 12/211,853 of Bober et al. and U.S. patent application Ser. No. 12/331,768 of Mandel et al., incorporated by reference above). Such modular printing systems can print multi-page documents, having both single color and multi-color pages, in simplex and/or duplex formats. To ensure that the various single and multi-color pages are printed on print media sheets by the appropriate printing engine(s), a sorting process is performed. Once printed, the single color and multi-color pages are merged in order to output the finished document with all pages in the proper order. However, timing of sheet output from the different print engines to ensure proper page merging presents a problem for a number of reasons. For example, since multi-color print engines are typically more costly to run and since multi-page documents typically have significantly more text-only pages than multi-color pages, it is more cost efficient to print all or batches of multi-color pages together. This minimizes the number of on-off and warm-up cycles performed by the multi-color printing engine during a single print job, but results in multi-color pages being printed out of order and, particularly, early. One solution to this problem is to add a multi-sheet buffer module. Such a buffer module can be configured to pull, from a stream, sheets which have been printed early, to hold those sheets, and to subsequently insert those sheets back into the stream at the proper time.
In view of the foregoing, disclosed herein are embodiments of a multi-sheet buffer module and a modular printing system incorporating such a multi-sheet buffer module. The multi-sheet buffer module is configured with a primary sheet transport path that extends horizontally across a support frame from an input port to an output port. Vertically oriented parallel sheet buffer paths extend downward and upward from the primary sheet transport path. Each buffer path connects to a secondary sheet transport path, which provides a loop back connection to the primary sheet transport path. A stream of sheets will enter the primary sheet transport path at the input port. As the stream moves in the direction of the output port, sheets printed out of order and, particularly, early will be selectively diverted into the sheet buffer paths. At the proper moment, the sheet buffer paths will feed the buffered sheets into the secondary sheet transport path(s), which will transport them back to the primary sheet transport path such that they are inserted at the proper locations back into the stream of sheets. By orienting the sheet buffer paths in this manner, the width of the sheet buffer module can be decreased, while keeping constant or increasing the sheet buffering capacity.
Specifically, an embodiment of a multi-sheet buffer module can comprise a frame having a first side and a second side opposite the first side. This module can comprise a middle sheet transport path (i.e., a primary sheet transport path), upper and lower sheet transport paths (i.e., secondary sheet transport paths) and upper and lower sheet buffer paths. The middle sheet transport path can extend essentially horizontally across the middle of the frame from a sheet input port on the first side to a sheet output port on the second side. The upper sheet transport path can be above the middle sheet transport path. The lower sheet transport path can be below the middle sheet transport path. The upper sheet transport path and the lower sheet transport path can each have a first portion aligned with and approximately parallel to the middle sheet transport path and a second portion connected to the middle sheet transport path adjacent to the sheet output port. That is, the second portion of both the upper sheet transport path and lower sheet transport path can provide a loop back connection to the middle sheet transport path.
The upper sheet buffer paths can extend essentially vertically from the middle sheet transport path to the first portion of the upper sheet transport path. Similarly, the lower sheet buffer paths can extend essentially vertically from the middle sheet transport path to the first portion of the lower sheet transport path. Configuring the sheet buffer paths in this manner ensures that any sheet transported from the middle sheet transport path through a sheet buffer path and into either the upper sheet transport path or the lower sheet transport path will re-enter the middle sheet transport path adjacent to the sheet output port. Each sheet buffer path can have a length sufficient to hold one or more print media sheets. Furthermore, the upper and lower sheet buffer baths can have different lengths and thereby different buffering capacities.
In operation, a stream of sheets (e.g., sheets printed by a modular printing system that provides for single color printing in simplex or duplex format, multi-color printing in simplex or duplex format and, optionally, mixed printing) are fed into the sheet input port of the sheet buffer module. The middle sheet transport path receives the stream of sheets at the sheet input port. Then, as the stream of sheets is being transported by the middle sheet transport path in the direction of the sheet output port, at least one sheet buffer path of the upper and/or lower sheet buffer paths diverts at least one selected sheet from the stream (e.g., a sheet that was printed out of order and, particularly, early), holds that selected sheet, and subsequently feeds that selected sheet to the corresponding upper or lower sheet transport path at the proper moment such that, as that selected sheet re-enters the middle sheet transport path, it is inserted back into the stream at a predetermined point (i.e., at the proper location within the document being printed).
To accomplish this, the buffer module can comprise a controller that is operatively connected to the middle sheet transport path and the upper and lower sheet buffer paths so as to control movement of the sheets within the buffer module. Specifically, each sheet buffer path can have a corresponding gate and one or more sheet transport devices. The gate can be selectively controlled (e.g., by the controller) to force selected sheets to enter the sheet buffer path from the middle sheet transport path on demand. Additionally, the one or more sheet transport devices can be selectively controlled (e.g., by the controller) to force sheets, which are being held, to exit the sheet buffer path on demand.
The above-described multi-sheet buffer module embodiment can be incorporated into any modular printing system requiring sheet buffering in order to output a finished document with all pages in the proper order (e.g., a modular printing system that provides for single color printing in simplex or duplex format, multi-color printing in simplex or duplex format and, optionally, mixed printing (i.e., one side of a sheet printed in a single color, the opposite side of the same sheet printed in multiple colors)). Such a modular printing system can comprise a first printing engine module (e.g., a multiple color printing engine module) and a second printing engine module (e.g., a single color printing engine module) positioned adjacent to the first printing engine module (e.g., stacked on top of the first printing engine module). Sheets for a multi-page document printed by the first print engine module and/or the second print engine module can be merged and fed in single stream into the sheet input port of the sheet buffer module. As described in detail above, the buffer module can be configured to divert selected sheet(s) from the stream (e.g., any sheet(s) that were printed out of order or, particularly, early), to hold the selected sheet(s), and to subsequently cause the selected sheet(s) to be inserted back into the stream at a predetermined point (i.e., at the proper location within the document being printed) prior to being output to, for example, a finishing module.
These and other features are described in, or are apparent from, the following detailed description.